Cured products comprising epoxy resins and additional adhesives are widely used in many industrial fields, since they exhibit excellent thermal, mechanical, electric and adhesive properties. In particular, blended molding materials of epoxy resins and fillers are widely used as adhesives, insulating materials or structural materials for electronic or electric equipment, and played a part in making the equipment compact, improving reliability and increasing productivity.
During the past few years, due to the high performance, compact and light weight of products in the electronic and transportation fields, such as aircraft and automobiles, materials having high heat and stress resistance are required.
In addition, protecting semiconductor elements from moisture and impact has undergone enormous advancement. The packaging mode is generally classified into two types, one using ceramics or metals and the other using epoxy resins or silicone resins. However, plastic resin packaging using epoxy resins is the main type, in view of the associated productivity and cost.
Recently, due to the high integration of semiconductors, while the size of a chip has become larger, the width of the component wires has become narrower. Accordingly, increased stress resistance properties to improve reflow and to decrease thermal stress generated during the use of the article are required.
Specifically, according to surface mounting technology, unlike the constitutional Dual In Line Package (DIP), the package should Withstand soldering conducted at temperatures above 215.degree. C., which requires highly heat resistance materials.
In view of such requirements, although the conventional epoxy resins have good mechanical and electric properties and advantages in productivity and cost, the heat resistant properties of the prior art epoxy resins are poor.
In order to solve such problems, the use of a polyimide having high heat resistance has been proposed, instead of using epoxy resins. However, polyimides have poor moldability, due to its non-dissolving and non-melting properties. Also, it is costly. In addition, bismaleimides represented by N,N'-4,4'-diphenylmethane bismaleimide having high heat stability require high temperature and long curing time.
Japanese Laid-open Patent Publication Nos.(Sho)54-142298, 62-53324, 62-270618, etc. disclose that epoxy resins are cured with reaction initiators having functional groups such as --COOH, --OH, --NH.sub.2, and the like, at the imide backbone terminal to increase the thermal properties of the resin compositions.
Japanese Laid-open Patent Publication Nos.(Sho)58-215452, 58-89619, 59-64660, 59-227924 and 62-227917 disclose that compounds having amino groups at the terminal such as p- or m-aminophenol or diaminodiphenylmethane are reacted with conventional maleimides to obtain a prepolymer, and the resulting prepolymer is added to the resin compositions to react the remaining amino groups with the epoxy groups of the resin compositions, whereby the heat resistance of the resin composition is improved. However, the said prior art has limitations in controlling the reaction level and increasing the contents of imide groups. In addition, stress resistance of the resin compositions obtained from the prior art is decreased, since the stress is increased by the addition of maleimides, which are thermal properties modifiers.
Japanese Laid-open Patent Publication Nos.(Sho) 63-35626, etc. disclose a method for preparing thermal and mechanical properties modifiers by reacting siloxane diamines with acid anhydride, such as pyromelitic anhydride for biphenyltetracarboxylic dianhydride, or by reacting siloxanes having a terminal anhydride with diamine-based curing agents in the simple form. However, they are costly and difficult to handle in preparing a resin silant.
In order to solve the above-mentioned problems, we have extensively studied the relevant technology. As a result, we noted that the use of curing agents capable of simultaneously reacting with epoxy groups of epoxy resins and maleimide groups of maleimide-modified siloxane modifiers provides epoxy resin compositions having excellent heat resistance, stress resistance, processability and applicability.